Is it a Macs 7.5CC or 8.5CC?

The YS-45 is a BEAST (as you probably already know) on a pipe! Pinching the line is a hassle, especially if the stuff is under the cowl--

Another trick I use on my F-90/ OS-160FX combo is to close the needle valve when filling to avoid flooded-ness [X(] Would work probably on the YS also right up until you start- Just remember that setting!